The use of sulfur cure accelerators to increase the curing rate of rubber comositions and to thereby improve scorch safety at processing temperatures has long been practiced in the rubber industry.
Thus, for example, U.S. Pat. No. 3,947,511 (Raasch) discloses two classes of compounds useful as sulfur cure accelerators: (1) those of the formula: ##STR1## wherein X is alkyl; and (2) those of the formula: ##STR2## wherein X is alkylene, O- or S-interrupted alkylene, alkenylene, alkylenebis(arylene), arylenebis(alkylene) or arylene.
However, while such prior art sulfur cure accelerators will reduce the cure time and consequently improve scorch safety, it would nonetheless be desirable to possess novel cure accelerators which would further improve scorch safety. It would also be desirable to possess sulfur cure accelerators that would produce cured rubber compositions having enhanced physical properties relative to rubbers cured employing such prior art sulfur cure accelerators.
Coran (U.S. Pat. No. 3,546,185) shows the use of specified sulfenamides which function as inhibitors of premature vulcanization. As is stressed in Coran (see, e.g. column 2, lines 43-45) such inhibitors are employed in combination with an accelerator to increase scorch safety by retarding cure.
Matoba (U.S. Pat. No. 4,268,640) discloses a curable composition comprising a halogen-containing polymer and a substituted mono- or di-thiobiurea which functions as a cross-linking agent.
It is an object of this invention to provide novel cure accelerators which would provide increased scorch safety in the production of cured rubber compounds.
It is a further object of this invention to provide a curable rubber composition which incoporates such improved sulfur cure accelerators.
It is another object of this invention to provide a sulfur cure accelerator which, when employed in rubber, will produce rubber compositions having desirable elastomeric properties.
The foregoing objects and additional objects will become more fully apparent from the following description and accompanying Examples.